Field
The present invention relates to microelectromechanical devices and specifically to an inertial sensor with self-test capability and a self-test method for an inertial sensor.
Description of the Related Art
Capacitive microelectromechanical sensors have become part of many consumer devices and they are used also in a variety of safety critical applications. Especially in the latter case, it is important to identify potential failures in mechanical or electrical signal paths of the capacitive sensor.
In capacitive sensors, acceleration-like self-test signals can be generated using electrostatic forces. However, in order to mimic the full-scale acceleration induced motion of the micromechanical proof mass, voltages higher than nominal supply voltage are typically needed.
High voltages should preferably be generated locally because external high-voltage sources are often not available, especially in field conditions. On-chip generation of variable high-voltages is, however, often area consuming because high-ohmic resistive feedback is needed in order to scale down and control the magnitude of the generated high-voltage. Additionally, any discrete time circuitry or logic in high-voltage domain easily draws additional current. In some cases, high-voltage switches and logic increase complexity of the device because of limited gate-source voltage tolerance in switch transistors. Furthermore, use of resistors consumes not only circuit/chip area, but also power, because the pump needs to supply the current that flows through the resistive dividers. Large capacitors for enabling large current consumption from a charge pump circuitry consume significant circuit/chip area, and should be avoided.